The invention relates to a coal-fired power plant or station having a boiler that can be heated by a dry firing, and with a flue gas channel that adjoins the boiler and that leads to a catalytic converter for reducing the NOx level.
During dry firings, the ash is produced as dry dust that is partially withdrawn at the bottom out of the combustion chamber, but also is partially carried along by the flue gas stream. The catalytic converter for reducing the NOx level comprises packings of narrow channels, and the carried-along dust has the tendency to accumulate on the catalyzer surfaces. This leads to the channel walls increasingly losing their catalytic effect. One is therefore forced to clean off the catalytic converters frequently with the use of soot blowers or also by the use of ultrasound. However, it was found that nevertheless the tendency existed for the catalyzer channels to become obstructed or clogged, and in particular in such a way that the obstructions could no longer be eliminated with conventional means.
In addition to a reduction of the catalytic effect, the pressure loss was increased due to the reduction of the flow cross-section. Similar obstruction effects were observed on the downstream air preheater, which operates in a regenerative manner. The pressure loss can become so great that the electrostatic filter, which is disposed downstream of the air pre-heater, reaches its limit of stability or resistance due to the induced-draft blower that follows. This can cause the load of the power station to be reduced, a measure that is a disadvantage and in addition, of course, does not represent a permanent solution. Rather, sooner or later the power station must be shut down in order to replace the clogged catalytic converters. However, even in the disassembled state elimination of the obstructions is not very practicable.
It is therefore an object of the invention to be able to protect the catalytic converter for reducing the NOx level against such obstructions in a simple and effective manner where such obstructions can no longer be eliminated with conventional means.